Position detecting apparatus

ABSTRACT

A position detecting apparatus is used with an exposure apparatus for projecting a mask pattern onto a substrate. The position detecting apparatus detects a position of an alignment mark formed on the substrate by sending light through a film having a wavelength-selective feature. The position detecting apparatus comprises a light sending system for emitting the position detecting light, a wavelength changing means for adjusting a wavelength band of the position detecting light directed onto the alignment mark, on the basis of the wavelength transmittance of the film having the wavelength-selective feature, and a light receiving system for detecting the light from the alignment mark. The position of the alignment mark can be determined on the basis of a photoelectric conversion signal outputted from the light receiving system.

This application is a division of prior application Ser. No. 08/869,220filed Jun. 4, 1997 U.S Pat. No. 6,100,987, which is a continuation ofprior application Ser. No. 08/409,095 filed Mar. 23, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a position detecting apparatus, andmore particularly, it relates to an alignment apparatus forphotoelectrically detecting positions of alignment marks on a substratesuch as a semiconductor element or a glass plate through photosensitivematerial such as photoresist in an exposure apparatus used in themanufacture of semiconductor elements or liquid crystal display elementsthrough a lithographic technique.

2. Description of the Related Art

In exposure apparatuses such as steppers or step-and-scan projectionexposure apparatuses, there is provided an alignment apparatus forperforming alignment between a reticle (or a photomask and the like) onwhich a pattern to be transferred is formed and a wafer (or a glassplate and the like) on which photoresist is coated with high accuracy.In order to perform such alignment with high accuracy, it is necessaryto correctly detect positions of wafer marks on the wafer.

In this regard, since roughness of a surface of the wafer is changedafter an exposure operation and subsequent processes and since heightsof the wafer marks in respective layers on the wafer often differ from aheight of a background, it is difficult to correctly detect thepositions of all of the wafer marks by using a single alignment system.

Accordingly, in the past, the following alignment systems have been usedfor various purposes:

(1) Alignment System of LSA (Laser-Step-Alignment) Type:

In this alignment system, a laser beam is directed onto a wafer mark,and light diffracted and scattered from the wafer mark is used tomeasure a position of such a wafer mark. This alignment system has beenwidely used regarding a wafer which is being processed.

(2) FIA (Field Image Alignment) System:

This alignment system is a sensor in which an enlarged image of a wafermark obtained by directing light having a wide wavelength band (emittedfrom a light source such as a halogen lamp and the like) onto the wafermark is picked up by an imaging element (such as a vidicon tube or aCCD), and an obtained image signal is image-treated to measure aposition of the wafer mark. This system is particularly useful for themeasurement of asymmetrical wafer marks on an aluminium layer or a wafersurface. This FIA system is disclosed in co-assigned patent applicationU.S. Ser. No. 841,833 filed on Feb. 26, 1992, for example.

(3) LIA (Laser Interferometric Alignment) System:

This alignment system is a sensor in which two laser beams havingslightly different frequencies are directed onto a diffraction gratingwafer mark from two directions, and two diffraction light beamsgenerated are interfered with each other to generate interference light.From the phase of this light position information of the wafer mark isdetected. This LIA system is effective for wafer marks having a smallheight difference or wafer marks having rough surfaces. The principle ofdetection in the LIA system is disclosed in U.S. Pat. No. 4,710,026 andco-assigned patent application No. U.S. Ser. No. 418,260 (filed on Oct.6, 1989), for example.

In the past, these various alignment systems have been used properly inaccordance with their purposes. Regarding wafers used in the exposureapparatuses, since a photoresist layer having a thickness of about 0.5-2μm is normally formed on the entire surface of the wafer, ifmonochromatic light is used as alignment illumination light or laserbeam, interference fringes are generated due to the monochromatic light,thereby causing a detection error when the position of the wafer mark isdetected. In order to suppress the interference phenomenon, alignmentillumination light of multi-wavelengths has been used or a band of thealignment illumination light has been widened.

For example, in the FIA systems of image pick-up type, a halogen lamp isused as an illumination light source. When a width of a wavelength band(except for a photosensitive band to the photoresist) of theillumination light is selected to be about 300 nm, the light reflectedfrom the surface of the photoresist layer does not substantiallyinterfere with the light reflected from the surface of the wafer, withthe result being that a sharp image can be detected. Accordingly, in theFIA system, only by using white illumination light (having a wide band)and by adopting achromatism of a focusing optical system, the positionof the wafer mark can be detected very accurately without beinginfluenced by the photoresist layer.

In this regard, conventionally, since the photoresist layer is made ofmaterial having good permeability to light other than violet/ultravioletlight (exposure wavelength band), red/near-infrared light has been usedmainly as the alignment illumination light so as not to sensitize thephotoresist. Thus, for example, even when the width of the wavelength isselected to be 300 nm, a light band having a main wavelength of about650 nm has been used, and a wavelength near the exposure wavelength hasnot been used to prevent the photoresist from being sensitized.

Also regarding the LIA systems, a technique has been proposed in whichan influence of film interference of the photoresist layer is reduced bydirecting a plurality of pairs of laser beams having differentwavelengths onto a diffraction grating wafer mark.

As mentioned above, in the conventional alignment systems, the influenceof the interference of the photoresist layer is reduced by widening thebandwidth of the alignment illumination light or laser beam within thered/near-infrared wavelength range or by polychromatizing theillumination light.

However, recently, for example, when color liquid crystal panels orcolor CCDs are manufactured, in consideration of the fact thatphotoresist having low permeability to the red/near-infrared wavelengthmay be used, it has been required that a position of an alignment markcan be detected through a film having low permeability to thered/near-infrared wavelength.

That is to say, for example, in the manufacture of the color liquidcrystal panels or color CCDs, red, green, blue or black photoresist(referred to as “color photoresist” hereinafter) materials are oftenused as the photoresist, and a color filter such as a red filter, agreen filter or a blue filter is often used. In the case where such acolor photoresist layer or color filter is used, when superimposingexposure is effected, the positions of the alignment marks providedunder the color photoresist layer or color filter must be detected.

However, when the red/near-infrared light is used as the illuminationlight from the alignment system, since the red/near-infrared light isabsorbed if the blue photo-resist or blue filter is used, there arises aproblem in which the position of the alignment mark cannot be detected.Accordingly, when the red/near-infrared light is used as the alignmentlight, as in the conventional case, depending on the colored thin filmssuch as the color photoresist or the color filter to be used, theabsorption of light occurs thereby making the detection of the wafermark position impossible.

SUMMARY OF THE INVENTION

The present invention solves the abovementioned conventional problems,and an object of the present invention is to provide a positiondetecting apparatus wherein, even when a film having awavelength-selective nature, i.e., a photosensitive layer or a filmhaving different permeability distribution features for respectivewavelengths is coated on alignment marks on a substrate, positions ofthe alignment marks can be correctly detected.

It is another object of the invention to provide a projection apparatuswherein, even when a film (color film) having wavelength-selectivenature covers alignment marks on a substrate, a mask and the substratecan be aligned with each other accurately for exposing a photoresistlayer on the substrate to the image of the pattern of the mask.

It is further object of the invention to provide a micro-device wherein,even when a film (color film) having wavelength-selective nature coversalignment marks on a substrate, the alignment marks can be detected forproducing the micro-device on the substrate.

According to the present invention, the following position detectingapparatus is provided. That is to say, there is provided a positiondetecting apparatus for detecting alignment marks formed on a substratethrough a film having a wavelength-selective nature. The positiondetecting apparatus comprises a light sending system for directingposition detecting light onto the alignment mark on the substratethrough the film having the wavelength-selective nature, a wavelengthchanging member for adjusting a wavelength band of the positiondetecting light directed on the alignment mark in accordance with thewavelength permeability feature (spectral sensitivity) of the filmhaving wavelength-selective nature, and a light receiving system fordetecting the light from the alignment mark, where the position of thealignment mark is detected on the basis of a photoelectric conversionsignal outputted from the light receiving system.

According to the above-mentioned position detecting apparatus, when amicro-device, such as a normal semiconductor element is manufactured,photoresist having high permeability to red/near-infrared is used asphotosensitive material, and any film which may absorb the positiondetecting light is not used. The wavelength changing member sets thewavelength band of the light directed onto the alignment mark to be thenormal red/near-infrared band. On the other hand, in the case where amicro-device, such as color liquid crystal display, color CCD and thelike is manufactured, when photoresist (blue photoresist) having highpermeability to blue light and low permeability to red light andtherearound is used as photosensitive material, or when the position ofthe alignment mark must be detected through a blue filter, thewavelength changing member sets the wavelength band of the lightdirected onto the alignment mark to be in the proximity of a blue lightband. By setting the wavelength band in this way, the position of thealignment mark can be detected correctly without sensitizing thephotosensitive material by the position detecting light.

The present invention further provides the following position detectingapparatus. That is to say, there is provided a position detectingapparatus used with an exposure apparatus for projecting a mask patternonto a substrate on which photosensitive material is coated and adaptedto detect alignment marks formed on the substrate through a film havinga wavelength-selective nature, and comprising a light sending system fordirecting light having a wide band passing through a plurality of filmseach having a wavelength-selective nature and used in the exposureapparatus onto the alignment mark on the substrate, a light receivingsystem for detecting the light from the alignment mark, and an adjustingdevice for changing the intensity of a photoelectric conversion signaloutputted from the light receiving system, in accordance with a kind ofthe film having wavelength-selective nature on the substrate, and theposition of the alignment mark is detected on the basis of thephotoelectric conversion signal outputted from the light receivingsystem.

According to this position detecting apparatus, the exposure apparatusin which the position detecting apparatus is previously incorporated isused as a special use apparatus for substrates on which either one oftwo kinds of color photoresist (blue photoresist or green photoresist)is coated. The illumination light (emitted from the light sendingsystem) having the wide band including a light with a wavelengthpermeable through these two color photoresist layers is directed ontothe alignment mark on the substrate. In this case, since the lightintensity of the reflected light is changed in depending upon the kindof the color photoresist actually coated on the substrate, the intensityof the photoelectric conversion signal from the light receiving systemis optimized by using the adjusting member. In this way, even wheneither one of these two color photo-resist is provided on the alignmentmark, the alignment mark can be correctly detected. Similarly, even wheneither one of more than 2 color filters of different colors is providedon the substrate, the alignment mark can be detected correctly throughthe color filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic constructural view of a projection exposureapparatus in which a position detecting apparatus according to apreferred embodiment of the present invention is incorporated; and

FIG. 2 is a schematic illustration for explaining an imaging element,where a section (a) is a plan view of an image observed by an imagingelement 39X of FIG. 1 and a section (b) is a chart of an image signalcorresponding to the image shown in the section (a).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, a position detecting apparatus according to a preferred embodimentof the present invention will be explained with reference to theaccompanying drawings. FIG. 1 shows an example in which a projectionexposure apparatus is used to manufacture a semiconductor element byutilizing a wafer as a substrate. Accordingly, in the explanation of theconstruction of the projection exposure apparatus which will bedescribed hereinbelow, alignment marks provided on the substrate arereferred to as “wafer marks”. The projection exposure apparatus shown inFIG. 1 is also used to other micro-devices, such as liquid crystaldisplay, CCD and thin film magnetic head using a glass plate as asubstrate.

FIG. 1 shows the projection exposure apparatus according to thepreferred embodiment. In FIG. 1, during exposure, exposure light IL(such as “i” radiation and excimer laser beam) emitted from anillumination optical system 11 is uniformly directed onto a pattern areaPA of a reticle R secured to a reticle holder 12 so that a pattern inthe pattern area PA is projected onto each of shot areas on a wafer W(or a glass plate) on which photoresist is coated, through a projectionoptical system PL. Prior to the exposure, it is necessary to correctlyperform alignment between a center of the pattern area PA and a centerof the shot area on the wafer W to be exposed.

The wafer W is rests on a wafer stage 13. A Z axis is selected to beparallel with the optical axis of the projection optical system PL, andan X axis is selected to be parallel with a plane of FIG. 1 in a planeperpendicular to the Z axis and a Y axis is selected to be perpendicularto the plane of FIG. 1. The wafer stage 13 comprises a Z-stage forfinely shifting the wafer W in the Z direction, a levelling stage foradjusting an inclination angle of the wafer W, and an XY-stage forpositioning the wafer W in the X and Y directions. An L-shaped movablemirror 14 is secured to the wafer stage 13. An X-coordinate and aY-coordinate of the wafer stage WS is always measured by using hemovable mirror 14 and an external laser interferometer 15, and themeasured coordinate values are sent to a main control system 16. Themain control system 16 serves to control the coordinate values of thewafer stage 13 shifted by a drive system 17, on the basis of thecoordinate values sent from the laser interferometer. A keyboard 18through which an operator can input information such as a kind ofphotoresist, various commands and the like is connected to the maincontrol system 16.

In order to detect a position of each of the shot areas on the wafer W,alignment wafer marks for the X axis and alignment wafer marks for the Yaxis are provided in connection with each shot area. In FIG. 1, as anexample, the wafer mark 32X for the X axis is illustrated. Prior to theexposure, the coordinate values (in a stage coordinate system)determined by the coordinate values of each wafer mark measured by theinterferometer 15 are detected by an alignment system 19, and alignmentregarding the corresponding shot area is performed on the basis of thedetected coordinate values.

The wafer mark 32X according to the illustrated embodiment comprisesrugged line-and-space patterns (multi pattern) spaced apart from eachother in the X direction by a predetermined pitch (refer to FIG. 2), andthe shape of a wafer mark for the Y axis corresponds to what is obtainedif the wafer mark 32X is rotated by 90 degrees. These wafer marks areprovided on scribe lines disposed on each shot area.

The alignment system serves to detect such wafer marks, and, in theillustrated embodiment, an FIA system, i.e., image processing typealignment system 19 of off-axis type is used. In FIG. 1, theillumination light from a halogen lamp 20 is directed to the alignmentsystem 19 through an optical fiber 21. In this case, the illuminationlight emitted from one end of the optical fiber 21 enters a collimatorlens system 24 through a wavelength selecting filter plate 22 and an NDfilter plate 23. The wavelength selecting filter plate 22 is formed by aplurality of interference filters through which different wavelengthscan pass and which are attached to a circular disc. By rotating thecircular disc by a drive motor 26, a desired wavelength band in theillumination light emitted from the optical fiber 21 can be selected.

The ND filter plate 23 comprises an optical filter which is attached toa circular plate and has the transmittance which is continuously changedwithin a predetermined range. By rotating the circular disc by a drivemotor 27, the intensity of the illumination light passing through thewavelength selecting filter plate 22 can be attenuated to a desired ratewithin the predetermined range. Rotational angles of the drive motors26, 27 are adjusted by an alignment light adjusting system 28 to whichthe main control system 16 and a memory 29 are connected. Informationregarding wavelength transmission features (spectral sensitivity) of anumber of photoresist layers, and information regarding wavelengthtransmission features of color filters are stored in the memory 29.

The illumination light is changed by the collimator lens system 24 toparallel light beams AL which in turn pass through a half prism 25 andan objective lens 30 and are reflected by a prism mirror 31 to bedirected onto the wafer mark 32X on the wafer W in a substantiallyvertical direction. The light reflected from the wafer mark 32X isreturned to the half prism 25 through the prism mirror 31 and theobjective lens 30, and light reflected by the half prism 25 enters anindex plate 34 through a focusing lens 33, thereby focusing an image ofthe wafer mark 32X onto the index plate. That is to say, the index plate34 is disposed substantially in an conjugate relation to the objectivelens 30 and the focusing lens 33. Index marks 35X for X axis and indexmarks (not shown) for Y axis are formed on the index plate 34. As shownin the section (a) of FIG. 2 (referred to as “FIG. 2(a)” hereinafter),each index mark 35X for X axis includes two straight patterns extendingin the Y direction, and the index marks are spaced apart form each otherby a predetermined distance in the X direction. The image 32XP of thewafer mark 32X for the X axis is focused between the index marks 35X.

In FIG. 1, the light passing through the index plate 34 is directed toan imaging element (pick-up element) 39X for X axis and an imagingelement 39Y for Y axis (which imaging elements each comprises atwo-dimensional CCD element and the like) through a relay lens system36, a relay lens system 37 and a half prism 38, so that the image of theindex marks and the image of the wafer mark are focused on the X axisimaging element and the Y axis imaging element, respectively. Imagesignals SX, SY from the imaging elements 39X, 39Y are sent to analignment control system 40. In the alignment control system 40, theposition of the X axis wafer mark 32X is detected on the basis of theimage signal SX from the imaging element 39X, and the position of the Yaxis wafer mark is detected on the basis of the image signal SY from theimaging element 39Y. The results of the position detection are sent tothe main control system 16.

Explaining the position detecting operation in detail, as shown in FIG.2(a), an observation field 42X on the index plate 34 observed by theimaging element 39X is elongated in the X direction and includes thefocused image 32XP of the wafer mark sandwiched by the index marks 35X.In this regard, an illumination field stop (not shown) is disposed at aposition substantially in a conjugate relation to the wafer W in thecollimator lens system 24 of FIG. 1 so that an illumination area on thewafer W, i.e., the observation field 42X of FIG. 2(a), is defined by theillumination field stop. In this case, scan lines in the imaging element39X is set to be in the X direction, and, as shown in a section (b) ofFIG. 2 (referred to as “FIG. 2(b)” hereinafter), the image signal SXoutputted from the imaging element 39X corresponds to the index marks35X and the image 32XP of the wafer mark. The image signal SX is made tohave two values, for example, defined by appropriate threshold values sothat a deviation amount of the wafer mark image 32XP with respect to theindex marks 25X in the X direction is determined on the basis of twovalues of the signal. In the main control system 16, an X-coordinateposition of the wafer mark 32X is detected or calculated by adding anX-coordinate value of the wafer stage 13 to the deviation amount. AY-coordinate position of the wafer mark for the Y axis is detected inthe similar manner.

In FIG. 2(b), automatic gain control (AGC) is applied to the imagesignal SX so that an average level of the signal is maintained at apredetermined constant level. In this case, the reason why the indexmarks 35X are used is that there is a danger of drifting of a scan startposition of the imaging element 39X under various conditions.

In the illustrated embodiment, the image signals SX, SY outputted fromthe imaging elements 39X, 39Y are sent to a level detecting portion 41.In the level detecting portion 41, average values of the image signalsSX, SY are independently detected, and the data regarding the averagevalues is sent to the main control system 16. Since levels of the imagesignals SX, SY are controlled under the automatic gain control, if alight amount of the light reflected from the wafer mark exceeds a rangewhich can be controlled under the automatic gain control, the averagevalues detected by the level detecting portion 41 will be changed.

Next, the operation in the illustrated embodiment will be explained. Asan example, it is assumed that a glass plate is used as the substrateand a three-color filter for a color crystal panel is manufactured byusing photoresist (color photoresist) colored in blue (bluephotoresist). The color of the photoresist may be red, green, blue orblack. For example, when red photoresist is used, in FIG. 1, a liquidcrystal substrate on which the red photoresist is coated is provided inplace of the wafer W. In this case, the red photoresist is removed fromthe liquid crystal substrate at areas other than a predetermined windowportion by using exposing and developing processes so that a red filterexists in the predetermined window portion only. Other color resistlayers may be treated in the similar manner. Even when the color liquidcrystal panel is manufactured in this way, alignment marks are formed ineach of layers on the liquid crystal substrate. Thus, it is necessary todetect positions of the alignment marks through the color photoresistlayer coated on the alignment marks.

In this case, information data regarding wavelength transmission foreach of the red photoresist, green photo-resist, blue photoresist andblack photoresist are stored in the memory 29 of FIG. 1. Moreparticularly, the average transmittance data regarding wavelength bandsections obtained by dividing a visible wavelength band (having awavelength of 400-750 nm) and a near-infrared wavelength band (having awavelength of 750-1000 nm) by a unit of 10 nm, for example, are storedin the memory. Hereinbelow, the average wavelength transmittancedistribution is referred to as “spectral sensitivity”.

In this method, regarding the red photoresist, since red wavelength bandcan pass through the red photoresist layer as is in the normalphotoresist layer, there is no problem. That is to say, when theoperator inputs the fact that the red photoresist is now used to themain control system 16 via the keyboard 18, the main control system 16sends a command to the alignment light adjusting system 28 so that thewavelength band and intensity of the illumination light AL must beadjusted to be commensurate with the red photoresist. In correspondenceto this, in the alignment light adjusting system 28 of FIG. 1, the factthat the red wavelength band can be used is confirmed on the basis ofthe wavelength/transmission feature for the red photoresist stored inthe memory 29, and then, the interference filter through which the redlight can pass is aligned with the output end of the optical fiber 21 byrotating the wavelength selecting filter plate 22 by means of the motor26.

Thereafter, the data regarding the average value of the image signal SXdetected by the level detecting portion 41 is sent to the main controlsystem 16. If the average value smaller than or greater than apredetermined rated value range, the main control system 16 emits thecommand to the alignment light adjusting system 28 to cause the latterto adjust the light amount of the illumination light AL. In response tothis, in the alignment light adjusting system 28, the light amount ofthe illumination light passed through the wavelength selecting filterplate 22 is optimized by rotating the ND filter plate 23 by means of thedrive motor 27. In this way, the position of the alignment mark (markcorresponding to the wafer mark 32X) can be detected with a high NSratio and with high accuracy.

Thereafter, the alignment between the reticle and the substrate isachieved based on the detected position of the alignment mark so thatthe color photoresist on the substrate is exposed to the reticlepattern. By developing this substrate, a color photoresist image of aliquid crystal element is formed on the substrate.

In this case, in the alignment system 19, aberrations of various lenssystem (24, 30, 33, 36, 37) are corrected so that the aberrations becomesmall in the wavelength band from blue to near infrared. Due to thesecorrections, even when the wavelength of the illumination light ischanged or switched, the wafer mark image can be sharply focused ontothe imaging elements 39X, 39Y. However, if the chromatic aberration ofthe focusing system including the objective lens 30 and the lens system33 along its axis is still a problem, information regarding axialchromatic aberration for each wavelength can be previously stored in thememory 29 so that such chromatic aberration information is sent to themain control system 16. Then, the height of the substrate is adjusted bydriving the Z stage of the wafer stage 13 by the control system 16through the drive system 17 to cancel the axial chromatic aberration,thereby reducing the influence of the axial chromatic aberration.

In connection with the axial chromatic aberration, even when theobjective lens 30 has a telecentric feature (toward the substrate)regarding a predetermined reference wavelength, the telecentric featuremay be changed or destroyed for other wavelengths. If the telecentricfeature is destroyed depending upon the wavelength in this way, adestroyed amount of the telecentric feature can be previously stored inthe memory 29 for the central wavelength in each of wavelength bands. Inthis case, when the position of the substrate in the Z direction ischanged by the Z stage to correct the axial chromatic aberration for theband employed, the measured position of the alignment mark is correctedby the main control system 16 by an amount corresponding to thedestroyed amount of the telecentric feature for the central wavelengthof the employed band. In this way, the position of the alignment markcan always be detected with high accuracy.

Regarding magnification chromatic aberration of the alignment system 19,when a distance (base line) between a reference point in the observationarea of the alignment system 19 and the exposure center is determined,calibration regarding the magnification chromatic aberration may beeffected. More specifically, for each color photoresist, the base lineis measured in a condition that the illumination light having thewavelength corresponding to each color photoresist is directed onto areference mark (not shown) on the wafer stage 13, and the measuredresults for respective color photoresist layers are stored in thememory. Alternatively, the magnification chromatic aberration may bepreviously measured and be stored as data.

When the green photoresist or the blue photoresist is used, since anoticeable amount of the red light (normal alignment illumination light)is absorbed by the photoresist, the wavelength band must be changed.More specifically, when the blue photoresist is used, the wavelengthselecting filter plate 22 is rotated by the alignment light adjustingsystem 28 so that the interference filter through which the blue lightcan pass is aligned with the output end of the optical fiber 21. As aresult, the illumination light AL is not absorbed by the bluephotoresist, and, thus, an adequate amount of the light reflected fromthe alignment mark can reach the imaging element 39X. If a light amountof the blue illumination light is small, the transmission rate of the NDfilter plate 23 may be increased. Similarly, when the green photo-resistis used, green light may be used as the illumination light AL.

In this way, even when either one of the red photoresist, greenphotoresist and blue photoresist is used, the position of the alignmentmark can be detected correctly. Further, since the light other than thelight passing through the color photoresist is blocked, the colorphotoresist itself is not sensitized or excited by the alignmentillumination light AL. In addition, since the wavelength bands capableof passing through the respective color photoresist layers are wide andeach of the transmittable wavelength bands of the correspondinginterference filters in the wavelength-selective filter plate 22 has asubstantial width, the influence of the film interference of each colorphotoresist can be reduced.

When the black photoresist is used, since the transmittance of any lightcomponent in the visible light is low, the optimum wavelength havinghigh transmittance cannot be selected. Thus, in this case, thewavelength selecting filter plate 22 is set so that the wavelength bandof the illumination light AL is widened to increase the total lightamount within a wavelength range which does not sensitize the blackphotoresist. Further, the light amount of the illumination light AL isincreased by using the ND filter plate 23 so that the average value ofthe image signal detected by the level detecting portion 41 ismaintained within a rated range. In dependence upon the kind of theblack photoresist, when the near infrared wavelength band has atransmission area, the near infrared light may be selected by thewavelength selecting filter plate 22.

In the case where the black photoresist is used, when it is desired tosignificantly increase the light amount of the illumination light, forexample, a stop may be previously disposed between the halogen lamp 20and the optical fiber 21. In this case, during the normal operation, anopening rate of the stop is decreased to reduce the light amount of theillumination light.

Although the spectral sensitivity regarding the transmittance of each ofcolor photoresist layers is stored in the memory 29 in the projectionexposure apparatus of FIG. 1 so that all of the color photoresist layerscan be treated, respective projection exposure apparatuses may bedesigned so that each of the projection exposure apparatuses can exposeonly one color photoresist (or color filter), as well as the normalphotoresist, and the interference filter corresponding to the relevantcolor photoresist alone may be mounted on the wavelength selectingfilter plate 22 of each projection exposure apparatus. By adopting thistechnique, the arrangement can be simplified. In this case, the exposureregarding one color photoresist is performed by using one of theprojection exposure apparatuses, and the exposure regarding anothercolor photoresist is performed by using another projection exposureapparatus.

Alternatively, a first projection exposure apparatus may be designed totreat the blue photoresist and the green photoresist, for example, and asecond projection exposure apparatus may be designed to treat the redphotoresist and the black photoresist so that a different pair of colorphotoresist layers can be treated by each of two projection exposureapparatuses. As a first alteration, a first projection exposureapparatus may be designed to treat the blue photoresist, greenphotoresist and red photoresist, for example, and a second projectionexposure apparatus may be designed to treat the black photoresist, aswell as the normal photoresist. As a second alteration, a firstprojection exposure apparatus may be designed to treat the bluephotoresist alone, for example, and a second projection exposureapparatus may be designed to treat the green photoresist, redphotoresist and black photoresist.

In the above-mentioned embodiment, while an example that the wavelengthselecting filter plate 22 is set in accordance with the kind of thecolor photoresist inputted by the operator is explained, the optimuminterference filter in the wavelength selecting filter plate 22 may beautomatically selected in the following manner. That is to say, in orderto automatically select the optimum interference filter, for example,when a position of a first alignment mark on a first substrate among alot of substrates is detected, the wavelength band of the illuminationlight AL is gradually changed by rotating the wavelength selectingfilter plate 22 in a condition that the transmittance of the ND filterplate 2 is selected to be an intermediate value (about 50%). Then, theaverage value of the image signals detected by the level detectingportion 41 is monitored so that the light having the wavelength bandselected when the average value becomes maximum is determined as lightto be used, and the wavelength selecting filter plate 22 is fixed atthat position. Then, the ND filter plate 22 is rotated to properly setthe average levels of the image signals SX, SY.

Thereafter, under this condition so set, the positions of the remainingalignment marks on the current, substrate are detected, and then, thepositions of the alignment marks on the remaining substrates aredetected. In this technique, the positions of the alignment marks canaccurately be detected with high SN ratio.

In place of the fact that the kinds of the color photoresist and of thecolor filter are inputted by the operator to the main control system 16through the keyboard 18, an identifying code (for example, bar code)representative of information regarding the spectral sensitivity of thetransmittance of a film having wavelength-selective feature coated on asubstrate such as a wafer, a liquid crystal substrate or the like may beformed on the substrate or on a cassette containing such a substrate. Inthis case, the identifying code on the substrate or the cassette can beread by a bar code reader (not shown) and the read spectral sensitivityof the transmittance can be automatically supplied to the alignmentlight adjusting system 28. Alternatively, a “name” of a substrate alonemay be registered in a corresponding identifying code and thetransmittance of a film having wavelength-selective feature coated onsuch a substrate may be stored in the memory 29 of the alignment lightadjusting system 28 in correspondence to the “name” of the substrate.

In FIG. 1, while an example that the wavelength of the illuminationlight is changed by rotating the wavelength selecting filter plate 22 inaccordance with the transmittance of the film (such as colorphotoresist) having wavelength-selective feature is explained, in placeof this example, for example, light having a wide wavelength band(including multi wavelength light) including wavelengths capable ofpassing through two or more kinds of color photoresist layers may alwaysbe directed onto the substrate. In this case, in accordance with thekind of the color photoresist (i.e. in accordance with the wavelengthpassing through the photoresist), the average intensity of each of theimage signals SX, SY from the imaging elements 39X, 39Y is set to bewithin a predetermined limit level range.

In order to adjust the intensity of each of the image signals SX, SY, amethod for electrically changing amplitude of the signals under theaction of the automatic gain control (AGC), a method for changing alight emitting power of a light source for the light having a widewavelength band (including multi wavelength light) directed on thesubstrate, or a method for changing intensity of light incident to eachimaging element 39X, 39Y by using the ND filter plate 22 of FIG. 1 canbe used. For example, in an exposure apparatus which can treat the bluephotoresist and the green photoresist, light having a wide wavelengthband (including multi wavelength light) including a blue color and agreen color is directed on the substrate. In this case, if the signalintensity of the green photo-resist is considerably weaker than that ofthe blue photoresist, when the exposure apparatus is desired to be usedto treat the green photoresist, the intensity of the light having thewide wavelength directed onto the substrate may be increased. With thisarrangement, for example, the wave-length varying member including thewavelength selecting filter plate 22 shown in FIG. 1 can be omitted,thereby simplifying the entire apparatus.

In FIG. 1, while the ND filter plate 23 acting as the light intensitychanging member is disposed within the light sending system (the lightpath from the halogen lamp 20 for illuminating the mark on thesubstrate), such an ND filter plate 23 may be disposed between the relaylens system 37 and the half prism 38 in the light receiving path fromthe mark on the substrate to the imaging elements 39X, 39Y to change theintensity of the light incident to each imaging element 39X, 39Y.Furthermore, the light intensity changing member is not limited to theND filter plate 23 shown in FIG. 1. The same function may be achieved byany other suitable means, such as a stop having a variable aperture andan acousto-optic modulator utilizing the Raman-Nath diffraction(Debye-Sears effect).

While the operation regarding the illustrated embodiment is explained inconnection with the manufacture of the color liquid crystal panel as anexample, the present invention can be similarly applied to themanufacture of a color CCD, for example. Furthermore, although theillustrated embodiment is described assuming that a color photoresistshould be used, the foregoing embodiment can also be applied as it is tothe case where a color filter is interposed between a photoresist and asubstrate to attain the same effect.

In the illustrated embodiment, while an example that the halogen lamp isused as the light source for the alignment light is explained, an LED ora laser diode may be used as the light source. Further, the intensity ofthe illumination light may be adjusted by changing the electric powersupplied to such a light source.

In this regard, in the illustrated embodiment, while an example that thewavelength band of the alignment illumination light is widened by usingthe halogen lamp is explained, the illumination light may have multiwavelengths. In this case, it is desirable that each of the wavelengthsof the illumination light has a predetermined width (for example, about±10-±50 nm). Alternatively, the light source for the alignment light maybe constituted by a plurality of light sources having output wavelengthswhich differ from each other at least partially so that the light havingthe wide wavelength band or the light having the multi wavelengths canbe derived from these light sources.

In the illustrated embodiment, while the present invention is applied tothe FIA system of off-axis type, the present invention may similarly beapplied to an LIA system or an alignment system of LSA type. Of course,the present invention can be applied to an alignment system of TTL(through-the-lens) type or an alignment system of TTR(through-the-reticle) type. However, in the TTL alignment system or theTTR alignment system, since the chromatic aberration of the projectionoptical system PL may cause a problem, an aberration correcting plate(i.e. a transparent plate having a plurality of diffraction gratingscorresponding to the wavelength widths of the illumination light foralignment) may be disposed in the proximity of a pupil plane (Fouriertransform plane for the reticle R) of the projection optical system PLas shown in U.S. Pat. No. 5,204,535 so that the diffraction grating canbe switched or changed in accordance with the used illumination light tobring the axial chromatic aberration and the magnification chromaticaberration of the illumination light to zero or below a predeterminedlimit value by using the optimum diffraction grating. In this case, forexample, in order to treat three kinds of color photoresist layers,three sets of diffraction gratings for the respective colors are formedon the transparent plate.

As mentioned above, the present invention is not limited to theabove-mentioned embodiment, but, various alterations and modificationscan be adopted within the scope of the present invention.

In the position detecting apparatus according to one aspect of thepresent invention, even when the photo-sensitive layer or film havingthe transmittance distribution for each wavelength different from thatof the previously used film is coated on the alignment wafer mark, thewavelength band of the position detecting illumination light can be setto be the wavelength band which cannot be absorbed by the film havingthe wavelength-selective feature. Accordingly, since the adequate amountof the light reflected from the alignment mark is directed to the lightreceiving system, the position of the alignment mark can be correctlydetected without exposing the photosensitive material.

Further, by providing the memory in which the wavelength transmittancevalues of the plural films having the wavelength-selective features arestored, and the input device for inputting the kind of the film havingthe wavelength-selective feature coated on the substrate, when thewavelength band of the alignment light is adjusted by the wavelengthchanging member on the basis of the stored wavelength transmittancecorresponding to the kind of the film inputted by the input device, thewavelength band of the alignment light can be correctly set manually.

On the other hand, by providing the light intensity detector fordetecting the intensity of each photoelectric conversion signaloutputted from the light receiving system, and the control means fordetermining the wavelength band of the alignment light suitable to thefilm having the wavelength-selective feature on the basis of theintensity detected by the light intensity detector when the wavelengthband of the light directed on the alignment mark is changed by thewavelength changing member, the alignment light having the optimumwavelength band can be selected automatically.

When the intensity of the alignment light directed on the alignment markis adjusted by the wavelength changing member in accordance with thewavelength transmittance of the film having the wavelength-selectivefeature, the NS ratio of the light received by the light receivingsystem can always be maintained to the high level.

In the position detecting apparatus according to another aspect of thepresent invention, since the light beams having wide wavelength bandspassing through a plurality of films (possible to be put on thesubstrate) having wavelength-selective features are directed onto thesubstrate and the intensity of each of the obtained photoelectricconversion signals is adjusted, even when the photosensitive layers orfilms having different wavelength transmission distributions are coatedon the alignment mark, the position of the alignment mark can bedetected correctly.

In addition, when the intensity of light is changed by using the lightintensity changing member in accordance with the transmittance of thefilm having the wavelength-selective feature, even if the transmittanceof the film having the wavelength-selective feature is greatly changed,the position of the alignment mark can be detected easily and correctly.

What is claimed is:
 1. A photo-lithographic system comprising more than one exposure apparatus including first and second exposure apparatuses, wherein the first exposure apparatus transfers a first pattern onto a substrate which has a first mark formed thereon, said first mark being covered with a first film having a light transmittance feature for transmitting light of a first wavelength band, said first exposure apparatus having a first detection device which directs a first illumination beam having a wavelength within said first wavelength band onto said first mark to attain information of the position of said first mark, and the second exposure apparatus transfers a second pattern onto said substrate which has a second mark formed thereon, said second mark being covered with a second film having a light transmittance feature for transmitting light of a second wavelength band which is different from said first wavelength band, said second exposure apparatus having a second detection device which directs a second illumination beam having a wavelength within said second wavelength band onto said second mark to attain information of the position of said second mark.
 2. A photo-lithographic system according to claim 1, wherein said first detection device has an interference filter for passing light of said first wavelength band, said first interference filter being disposed in the light path of said first illumination beam, and said second detection device has an interference filter for passing light of said second wavelength band, said second interference filter being disposed in the light path of said second illumination beam.
 3. A photo-lithographic system according to claim 1, wherein said second exposure apparatus selectively transfers second patterns onto a plurality of substrates each having said second mark, said second wavelength band including a plurality of different wavelength band sections, said plurality of substrates provided with said second marks being covered with respective films having light transmittance features for transmitting light of said different wavelength band sections, and said second detection device further includes a wavelength selection device which selects a wavelength band section for said second illumination beam so that the selected wavelength band section corresponds to the light transmittance feature of the film of a selected substrate, said second detection device directing said second illumination beam having a wavelength within the wavelength band section selected by said wavelength selection device onto said second mark.
 4. A photo-lithographic system according to claim 3, wherein said second detection device further comprises: a memory for storing information about light transmittance of said plurality of films of the different kinds with respect to different wavelengths; and an input device which inputs information regarding said kinds of the films, said wavelength selection device selecting the wavelength of said second illumination beam based on said information stored in said memory and said information about the kinds of films inputted through said input device.
 5. A photo-lithographic system according to claim 4, wherein said input device includes a setting device operable from the outside, said input device inputting information about the kinds of the film which is set by said setting device.
 6. A photo-lithographic system according to claim 3, wherein said wavelength selection device includes a plurality of interference filters having respective different transmission wavelength band sections and disposed in the light path of said second illumination beam, said wavelength selection device changing the wavelength of said second illumination beam to be directed onto said second marks by selectively positioning said plurality of interference filters in the light path of said second illumination beams.
 7. A photo-lithographic system according to claim 3, wherein said second detection device further comprises a light intensity adjusting system for adjusting the intensity of said second illumination beam based on said light transmittance features of said films with respect to different wavelengths.
 8. A photo-lithographic system according to claim 7, wherein said light intensity adjusting system adjusts the intensity of said second illumination beam after said wavelength selection device has selected an applicable wavelength.
 9. A photo-lithographic system according to claim 8, wherein said second detection device comprises a light directing system for directing said second illumination beam onto said second marks and a light receiving system for introducing the light returned from said second marks to a photo-electric conversion device, said light intensity adjusting system adjusting the intensity of said second illumination beam by changing the light emitting power of a light source of said light directing system or controlling an optical filter which is disposed in said light directing system to continuously attenuate the intensity of said second illumination beam in a predetermined range.
 10. A photo-lithographic system according to claim 1, wherein said first and second films comprise color resists coated on said substrates and having different colors.
 11. A photo-lithographic system according to claim 10, wherein said first film comprises a black resist.
 12. A method of producing a transferred-pattern-bearing device by using more than one exposure apparatuses, the method comprising the steps of: attaining information about a position of a first mark formed on a substrate by utilizing a first detection device provided in a first exposure apparatus for transferring a first pattern onto said substrate, said substrate having a first film over said first mark, said first film having a light transmittance feature for transmitting light of a first wavelength band, said first detection device attaining said information about the position of said first mark by directing a first illumination beam having a wavelength within said first wavelength band onto said first mark; transferring said first pattern onto said substrate by said first exposure apparatus after effecting alignment of said substrate based on said information about position of the first mark; attaining information about a position of a second mark formed on said substrate by utilizing a second detection device provided in a second exposure apparatus for transferring a second pattern onto said substrate, said substrate having a second film over said second mark, said second film having a light transmittance feature for transmitting light of a second wavelength band different from said first wavelength band, said second detection device attaining said information about the position of said second mark by directing a second illumination beam having a wavelength within said second wavelength band onto said second mark; and transferring said second pattern onto said substrate by said second exposure apparatus after effecting alignment of said substrate based on said information about position of the second mark.
 13. A method according to claim 12, wherein said second exposure apparatus is capable of selectively transferring second patterns onto a plurality of substrates each having said second mark, said second wavelength band including a plurality of different wavelength band sections, said plurality of substrates provided with said second marks being covered with respective films having light transmittance features for transmitting light of said different wavelength band sections, and said second detection device further includes a wavelength selection device which selects a wavelength band section for said second illumination beam so that the selected wavelength band section corresponds to the light transmittance feature of the film of a selected substrate, said second detection device directing said second illumination beam having a wavelength within the wavelength band section selected by said wavelength selection device onto said second mark.
 14. A method according to claim 13, wherein said second detection device further comprises: a memory for storing information about light transmittance of said plurality of films of the different kinds with respect to different wavelengths; and an input device which inputs information regarding said kinds of the films, said wavelength selection device selecting the wavelength of said second illumination beam based on said information stored in said memory and said information about the kinds of said films inputted through said input device.
 15. A method according to claim 14, wherein said input device includes a setting device operable from the outside, said input device inputting information about the kinds of the film which is set by said setting device.
 16. A method according to claim 13, wherein said second detection device further comprises a light intensity adjusting system for adjusting the intensity of said second illumination beam based on said light transmittance features of said films with respect to different wavelengths after said wavelength selection device has selected an applicable wavelengths.
 17. A method according to claim 16, wherein said second detection device comprises a light directing system for directing said second illumination beam onto said second marks and a light receiving system for introducing the light returned from said second marks to a photo-electric conversion device, said light intensity adjusting system adjusting the intensity of said second illumination beam by changing the light emitting power of a light source of said light directing system or controlling an optical filter which is disposed in said light directing system to continuously attenuating the intensity of said second illumination beam in a predetermined range.
 18. A method according to claim 17, wherein said first and second films comprise color resists coated on said substrates and having different colors.
 19. A transferred-pattern-bearing device manufactured by the method claimed in claim
 18. 